1. Field of the Invention
The invention relates to a backrest for a chair, more particularly to a backrest having a backrest cushion pivoted to a pivot shaft through a pair of pivoting members.
2. Description of the Related Art
A conventional chair, as shown in FIGS. 1 and 2, includes a seat member 11, a seat leg unit 12 disposed under a bottom of the seat member 11, and a backrest 2 extending upright from the seat member 11. The backrest 2 includes an L-shaped back support 21 having a top end portion provided with a rigid pivot shaft 213 that has two opposite end portions 214; a backrest cushion 22 disposed adjacent to the top end portion of the back support 21 and having a rear wall 221 that is formed with a pair of threaded holes 222; a coupling cover 23 made from a plastic material and having an open end 218 facing toward the rear wall 221 of the backrest cushion 22, covering the pivot shaft 213, and having a back wall 231 that is formed with a pair of counter bores 233; and a pair of screw bolts 24 extending respectively through the counter bores 233 in the back wall 231 of the coupling cover 23 and engaging threadedly and respectively the threaded holes 222 in the rear wall 221 of the backrest cushion 22 so as to drive the coupling cover 23 toward the backrest cushion 22 and to permit abutment of the open end 218 of the coupling cover 23 against the rear wall 221 of the backrest cushion 22. A pair of shaft-supporting plates 235 extend from the back wall 231 of the coupling cover 23, and are formed with end recesses 236 for receiving the end portions 214 of the pivot shaft 213, respectively.
When the chair 1 is in use, the user usually has his back abutting against the backrest cushion 22. When the user lying against the backrest cushion 22, the coupling cover 23, which engages the backrest cushion 22 through the bolts 24, will pivot about the pivot shaft 213 of the back support 21. The pivoting action will result in friction between the end portions 214 of the pivot shaft 213 and the shaft-receiving plates 235, which, in turn, can result in wearing of the shaft-receiving plates 235, thereby shortening the service life of the chair 1.